Lotus 7's (& clones) are classified into two categories, no aero mods and with aero mods, with different point values. How modified can a 7 with aero mods be and still be considered ST legal?

The reason is per the latest Solo clarification (yes, from the evil SCCA), a D or E Modified 7 can now have some significant front end aero mods.

Feb 2008 FASTRACK

TECH BULLETINS· Modified, per the MAC: Section 18.1.E.3 Front Aero, as it applies to the case of the Lotus Seven and similar cars with irregular front top view profiles for front spoiler/splitter construction - As an example, the Lotus Seven has a narrow central nosecone and separated front fenders. If a front spoiler wider than the nosecone were added, it would hang in free air. Air would flow both above and below the spoiler, meeting the definition of a wing, which would be an illegal configuration. However, the rules allow the front spoiler to be as wide as the rear bodywork of the car at axle height. A front spoiler/splitter only as wide as the nosecone would be of limited aerodynamic value. Furthermore, front aero is needed to balance rear aero; limiting one effectively limits the other. So, in the interest of parity, the Seven and similar cars are allowed to add a full width front spoiler. However, if you would add such a spoiler, you must fill in the front bodywork, closing the gaps between the nosecone, spoiler, and clamshell fenders, to avoid creating a “wing”. This will require adding bodywork filler panels for the car, and will change its look as it changes its function. The temptation might be to further optimize the cars front end for aero purposes, creating a sports racer-like wedge-shaped front using angled ramps to join the fenders to the spoiler/splitter assembly. This would exceed the parity intended by this allowance and is not allowed. Therefore, when a Lotus Seven or similar vehicle uses a full-width front spoiler, the car’s spoiler/ air dam is required to be vertical (between 80-100 degrees) for the lower 8” of its extent. The splitter is to be horizontal within +/- 3/16” over its length.Outside of these constraints, the builder may close off the front of the car in any manner necessary. The change in top view outline caused by these bodywork changes is allowed. The spoiler/air dam cannot be any wider than the rear bodywork at axle height. Splitters can extend 6 inches forward of the top view outline, but cannot extend wider than the top view outline.

I need to rebuild the 7 that was crashed at Barber, and would like to take the opportunity to incorporate a number of improvements, one being to improve the aero as allowed by the Solo rules (and hopefully the ST rules).

Yes, that 1.5 points difference hurts. But the acceleration really drops off over 100mph with the stock style (crappy) aero. I think the improved drag would really help (making up for some of the potential HP I have to give up), plus the downforce will help it in the corners.